The rockhopper penguins are three closely related taxa of crested penguins that have been traditionally treated as a single species and are sometimes split into two or three species.

Not all experts agree on the classification of these penguins. Some consider all three as distinct species, some split the western and eastern forms into the southern rockhopper penguin and keep the northern rockhopper as distinct, while other experts consider all three potential varieties to be one species.

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Rockhopper penguins are one of the smallest species of penguin in the world. They range from 2.3-2.7 kg where males are larger than females.[1] After reaching full growth, they are about 20 inches in height.[2] Males and females cannot be distinguished just by looks, so a DNA test is conducted by taking a feather from the bird to determine its gender.[1] Like many penguins, rockhopper penguins have a white belly and the rest of their body is black.[1] Some characteristics that differentiate them from the other penguins are their red eyes, orange beak, pink webbed feet, and the yellow and black spiky feathers they have on their head.[2][3] Although their yellow and black spiky feathers differentiate them from other penguins, rockhopper penguin chicks do not have them; these feathers develop with age.[3] Their orange beak is initially black, but as the penguins get older, their beaks turn orange.[3] Due to the harsh rocky environment, they cannot slide on their bellies like most penguins, so they hop to get from one place to another.[1]

What separates rockhopper penguins into subspecies is their location of reproduction and reproductive behaviors. The difference in mating signals found between the subspecies E. chrysocome (southern) and E. moseleyi (northern) seems to have occurred quickly, thus these behavioral changes are enough to isolate these taxa.[4]

Southern Rockhopper penguins are split into two subspecies and they are defined by their location of reproduction. The subspecies E. c. filholi (eastern) is known to reproduce in the sub-Antarctic around the Prince Edward Islands, Crozet Islands, Kerguelen Islands, Heard Island, Macquarie Island and Campbell, Auckland and Antipodes Islands. The subspecies E. c. chrysocome, which may be referred to the true southern subspecies, reproduces at offshore islands in southern Chile, Argentina and at the Falkland Islands. The Falkland Islands are known to have one of the largest populations of Southern Rockhopper penguins.[5]

Northern rockhopper penguins breed in cool temperate climates including on the islands of Gough and Tristan de Cunha in the Atlantic Ocean and St. Paul and Manchester in the Indian Ocean. The Southern rockhopper breeds on the Knutsford (cheshire) with breeding colonies around the Cape Horn of South America, the Falklands Island in the southern Atlantic Ocean, and Prince Edward, Marion, Crozet, Kerguelen, Heard, Macquarie, Campbell, Auckland and Antipodes Islands in the southern Indian Ocean. Eastern rockhopper penguins are mostly found breeding on Campbell Island in New Zealand, but their numbers have declined immensely.[6] Rockhopper penguins usually find their habitat in rocky shorelines. They make nests and burrows in tall grasses called tussocks.[7]

Rockhopper penguins are carnivorous birds, and they survive on marine animals.[1] Primarily, the rockhopper penguin’s diet consists of krill and small crustaceans, which may include crabs, lobsters, crayfish, or shrimp.[1] They also hunt larger organisms like squid and myctophid fish.[1][3] Rockhopper penguins eat more krill than they do fish; their diet changes when they migrate and as the seasons change.[3] Rockhopper penguins can be at sea for days while hunting. They can dive up to 330 feet (100 m) for several minutes at a time while looking for prey.[1]

Rockhopper penguins reproduce sexually with one male and one female. Rockhoppers are the most widespread crested penguins.[8] Their range goes from the Antarctic front to the South Atlantic and Indian Oceans.[8] Because of how widespread they are, breeding varies among the penguins in different areas. Northern Penguins begin the mating process two months earlier than Southern ones.[9] Two eggs are usually laid a few days apart during early November in hope that at least one will survive, and the second egg is usually larger than the first. They will use the same nest as they did in previous years as well. Eggs hatch about a month later and the mother will have food for the chick.[10]

There are currently 19 species and six genera of living penguins. The rockhopper penguin has 3 subspecies: Eudyptes filholi, the Eastern Rockhopper; Eudyptes mosleyi, the Northern Rockhopper; and the Eudyptes chrysocome, the Southern Rockhopper. They are separated by their locations of breeding. There are four other species in the Eudyptes genus: Eudyptes pachyrhynchus, Eudyptes robustus, Eudyptes chrysolophus, and Eudyptes schlegeli.[11] The three subspecies of the rockhopper penguin are believed to have split up because of latitude and watermasses rather than because of geographic distances. Research suggests that during the early Pleistocene, the Southern Ocean was cold and rockhopper populations from the Atlantic and Indian Oceans remained undifferentiated and lived in the same watermass. The mid-Pleistocene climatic transition was associated with the southward migration of frontal positions and islands became surrounded by subtropical water masses, resulting in a split between Northern and Southern rockhopper penguins. Many advance and retreat cycles of Patagonian icecaps during the late Pleistocene may have created a barrier to gene flow between Southern Pacific and Southern Atlantic populations, causing a split between Southern and Eastern rockhopper populations.[12]

Although the rockhopper penguin is one of the world’s most numerous penguin populations, it is estimated that the population has decreased almost 90% since the early 20th century.[2] The cause of this decline is mainly unknown, but scientists have speculated that humans are involved, mostly by commercial overfishing, oil exploitation, and pollution.[2][13] These activities have depleted much of the rockhopper penguin’s food supply and raised the sea surface temperatures, and because this species geographically is isolated to the tip of South America and the Falkland Islands and is very sensitive to food web changes, there is little foreseeable opportunity for the penguins to recover.[13][14]